Wireless Local Area Network (WLAN) technology is based on 802.11 Media Access Control (MAC) standards, which refer to a series of specifications developed by the Institute for Electrical and Electronic Engineers (IEEE). The MAC standards specify an over-the-air interface between a Station (STA) and an Access Port (AP).
FIG. 1 is a schematic illustrating a typical centralized WLAN network. As shown in FIG. 1, in the WLAN network, data are carried over wireless links between a STA and an AP, and are transmitted from the AP to an Access Controller (AC) through a wired network, the AC in turn forwards the data to an access network or to a destination AP and thereon to a destination STA.
FIG. 2 shows the procedure of controlling message interaction between an AP and an AC when an STA joins a wireless network. Specifically, the procedure is as follows.
Step 201: The STA gets on line, and broadcasts a Probe Request.
Step 202: The AP receives the Prove Request, and returns a Unicast Probe Response to the STA.
Step 203: The STA performs authentication to the AC via the AP.
The AP in step 203 is the one with the strongest Received Signal Strength Indication (RSSI) among a plurality of APs returning Unicast Probe Responses to the STA.
Step 204: If the authentication is successful, the STA sends an Association Request to the AC.
Step 205: The AC receives the Association Request and returns an Association Response to the STA.
Step 206: The AC starts providing service for the STA.
With dense deployments of APs becoming a tendency of market application, there may be multiple APs covering an area at the same time, so as to support features like fast roaming, location detection and RF (radio frequency) hole coverage. Coverage redundancy makes for a backup and also enhances network capacity.
Usually, the STA tends to join the WLAN network through an AP that is heard at highest RSSI. In other words, in an area that can be observed by the STA, even if there is more than one AP providing required wireless service, the STA tends to continue attempting to join the AP reflecting the highest RSSI. Hence there is a need for an important wireless feature: uniform distribution of STAs across APs in order to balance wireless loads.
At present, in order to balance wireless loads, most vendors control and limit number of STAs handled by each of the APs, which brings disadvantages as follows:
1. Only wired side traffic of an AP is taken into consideration at present, while wireless traffic flow of the AP is left out of account. Thus, load balance effect will be affected since wireless traffic flow is better at reflecting the AP's real traffic flow.
2. Each STA could contribute distinctly to the access network load. For instance, some STAs could be using the WLAN service for voice and some for video applications. So, using the number of STAs being serviced by each of the APs to balance the system load will not yield in an effective control.
3. Currently, an STA joins the wireless network through an AP with the highest RSSI at all time, and this innate feature of STA obstructs load balance.